Study Challenges Assumption That Summer Sun Restores Vitamin D Levels in High-Risk Groups
Key Insights
A Newcastle University study found vitamin D insufficiency (search) persisted year-round in older adults and minoritized ethnic groups in northern Britain, with no summer improvement.
More than half of adults aged 65 and older had insufficient vitamin D levels, with even higher rates among participants from minoritized ethnic backgrounds.
Researchers call for targeted public health strategies including clearer guidance, routine primary care assessments, and appropriate supplementation rather than relying on sunlight exposure.
A new study from Newcastle University's Human Nutrition and Exercise Research Centre is challenging the widely held assumption that summer sunlight exposure naturally restores vitamin D levels depleted during darker winter months. Published in the European Journal of Clinical Nutrition, the research found that vitamin D insufficiency (search) remained persistently high throughout the entire year among older adults and people from minoritized ethnic backgrounds living in northern Britain.
The findings carry significant implications for public health strategies aimed at preventing the long-term consequences of vitamin D deficiency, including osteoporosis (search), rickets (search), muscle weakness, and impaired immune function.
Persistent Deficiency Across All Seasons
Researchers analyzed vitamin D levels in nearly 300 participants recruited through community outreach and online methods across northern Britain. Each volunteer completed a simple finger-prick blood test, with samples analyzed by a specialist laboratory. The study focused on two populations: adults aged 65 and older, and individuals from minoritized ethnic backgrounds of all ages.
More than half of the older adults in the study had insufficient vitamin D levels. The proportion was even higher among participants from minoritized ethnic backgrounds. What most surprised the research team was that these levels showed little to no improvement during the summer months—a period when increased sunlight exposure would typically be expected to boost vitamin D production.
"What's striking about these findings is that vitamin D levels didn't improve, even in the summer months when we would usually expect them to recover," said Bernard Corfe, Professor of Human Nutrition and Health at Newcastle University and co-leader of the study.
Why Sunlight Alone May Not Suffice
Vitamin D is synthesized in the skin upon exposure to ultraviolet B (UVB) radiation from the sun. However, multiple factors can impair this process. Older adults produce vitamin D less efficiently than younger individuals. Skin pigmentation, clothing, sunscreen use, and geographic location all influence UVB absorption. In northern regions such as the North of England, sunlight is weaker for much of the year, further limiting natural vitamin D synthesis.
"For people living in places like the North of England, this shows that sunlight alone may not be enough, particularly for older adults and those from minoritized ethnic backgrounds," Corfe explained. "The message is simple but important. If you are in a higher-risk group, you can't assume that spending more time outdoors in summer will solve the problem."
Vitamin D plays a critical role in calcium absorption and bone health maintenance. Insufficient levels have been associated with a greater risk of osteoporosis (search), rickets (search), and weakened immune function. Growing research has also explored potential connections between vitamin D status and a range of chronic health conditions, though many of those relationships remain under investigation.
A Call for Targeted Public Health Measures
The researchers argue that the findings point to a need for more targeted public health strategies. They suggest that clearer guidance on vitamin D, brief vitamin D assessments during general practitioner appointments, and appropriate supplementation could help address what may be a largely unnoticed health issue.
"We need to be thinking about more consistent, year-round ways to support healthy vitamin D levels," Corfe said.
The study helps fill an important gap in understanding how vitamin D levels fluctuate throughout the year in populations known to face elevated deficiency risk. The next phase of the research will explore personalized and culturally appropriate strategies to improve vitamin D status, including tailored dietary recommendations and healthcare approaches designed to better meet the needs of different communities.
Study Design and Funding
The research was funded by Better You Ltd (search), a UK-based health and wellness company that manufactures and sells nutritional supplements. However, the funder had no role in designing the research, conducting the study, or interpreting the results. All aspects of the research were carried out independently by Newcastle University.
The study is registered under ISRCTN13778806 and was authored by Alice Goddard, Anthony Watson, Rowena Tilbury, Bernard M. Corfe, and Andrea Fairley, with a publication date of May 19, 2026.